Drug Interactions between Imitrex and UroAv-B

MONITOR CLOSELY: The following interaction applies only to products containing sodium biphosphate that are used for bowel cleansing. It does not apply to products containing sodium biphosphate that are used for other, non-laxative related purposes.

Coadministration with agents that affect renal function or perfusion such as diuretics, ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk of acute phosphate nephropathy associated with the use of bowel-cleansing phosphate solutions. The risk and/or severity of fluid and electrolyte disturbances may also be increased, which can lead to serious adverse events including cardiac arrhythmias, seizures, and renal impairment. Acute phosphate nephropathy is a rare adverse event that presents as acute renal failure with minimal proteinuria and a bland urine sediment. Renal biopsy findings are consistent with nephrocalcinosis and include acute and/or chronic renal tubular injury, calcium-phosphate crystal deposition in the distal tubules and collecting ducts, and no other pattern of histological injury. The risk of acute phosphate nephropathy stems from the large phosphate load, fluid shifts, and decreased intravascular volume, which can be exacerbated in the presence of medications that affect renal perfusion or function. In reported cases, acute renal failure was typically diagnosed within two to five months of colonoscopy. These cases often resulted in permanent impairment of renal function, some requiring long-term dialysis.

MANAGEMENT: Caution is advised when bowel-cleansing phosphate preparations are prescribed in patients treated with agents that affect renal function or perfusion, particularly if they are frail or elderly. Bowel-cleansing phosphate preparations should not be used in patients who have impaired renal function or perfusion, dehydration, or uncorrected electrolyte abnormalities. In patients at risk for acute phosphate nephropathy, baseline and postprocedure labs including serum electrolytes, calcium, phosphate, BUN, and creatinine should be performed. Patients should be advised not to exceed the recommended dosage of their bowel-cleansing preparation and to drink sufficient quantities of clear fluids during before, during, and after bowel cleansing. Limited data suggest that administration of an electrolyte rehydration solution may attenuate the electrolyte abnormalities and hypovolemia. Hospitalization and intravenous fluid hydration may be appropriate for frail or elderly patients who may be unable to drink an adequate volume of fluid.

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CONTRAINDICATED: Monoamine oxidase inhibitors (MAOIs) may significantly elevate the plasma concentrations of certain 5-HT1 receptor agonists (namely rizatriptan, sumatriptan, and zolmitriptan) and their active metabolites by inhibiting their metabolic clearance via monoamine oxidase, subtype A. Clinically, this interaction may increase the risk of vasospastic reactions, including coronary artery vasospasm, peripheral vascular ischemia and colonic ischemia, associated with the use of 5-HT1 receptor agonists. Although the pharmacokinetic alterations are observed only with a limited number of 5-HT1 receptor agonists and their metabolites, the possibility of a pharmacodynamic interaction should be considered for all agents in the class, since they exhibit modest 5-HT1A activity. Theoretically, MAOIs may potentiate the serotonergic activity of these agents and increase the risk of serotonin syndrome, which is a rare but serious and potentially fatal condition thought to result from hyperstimulation of brainstem 5-HT1A and 2A receptors. The mechanism is inhibition of the breakdown of serotonin by MAOIs. Symptoms of the serotonin syndrome may include mental status changes such as irritability, altered consciousness, confusion, hallucinations, and coma; autonomic dysfunction such as tachycardia, hyperthermia, diaphoresis, shivering, blood pressure lability, and mydriasis; neuromuscular abnormalities such as hyperreflexia, myoclonus, tremor, rigidity, and ataxia; and gastrointestinal symptoms such as abdominal cramping, nausea, vomiting, and diarrhea.

MANAGEMENT: Concomitant use of rizatriptan, sumatriptan, or zolmitriptan with MAOIs or other agents that possess MAOI activity (e.g., furazolidone, linezolid, methylene blue, procarbazine) is considered contraindicated. At least 14 days should elapse between discontinuation of MAOI therapy and initiation of treatment with 5-HT1 receptor agonists. If concurrent therapy is necessary, almotriptan, frovatriptan and naratriptan may be preferred due to the lack of a significant pharmacokinetic interaction with MAOIs. However, patients should be closely monitored for adverse effects related to excessive serotonergic activity.

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